Dry Packing

No activity at all today, and not much yesterday either, though one of the underpin pillars has now been "dry packed". The blockwork is built up to about 4 inches short of the foundations, and back filled with a very course concrete with steel grid-work inside. As you will have seen, pillars of this sort of height have to be built in stages to allow the concrete to go off properly so that there are no weak spots.

Anyway, the final 4 inches is "dry-packed". The Groundworks Contractor has explained this to me. The trouble with wet concrete is that it settles and drops in level. This is no use when it is supposed to be taking the weight of the house wall. Dry packing is when that last 4 inches is packed with a bairly wet concrete mix that is literally banged into place. Because it is dry, it does not settle and shrink back from the foundations. It takes in moisture from the air and surrounding material in order to cure. Result is a solid pillar that still meets the existing foundations. When the surrounding soil and rock is dug away for the next section, nothing should drop and crack - in theory !

I remember when I was a lad, my dad used to lay crazy paving on a dry mix, then go round with a watering can afterwards.